A conventional helicopter generally includes a main rotor assembly and a tail rotor assembly. A turbomachine is included with an output shaft configured to drive the main rotor assembly and tail rotor assembly. Typical turbomachines include a high pressure system, or core, in addition to a low pressure system. A low pressure shaft of the low pressure system is mechanically coupled to the output shaft through a gearbox for driving the output shaft, and in turn, the main rotor assembly and tail rotor assembly.
A rotational speed of the low pressure system relative to the core may be reduced due to a drag on the low pressure system from the main rotor assembly and tail rotor assembly. However, in the event of a loss of load failure, such as an output shaft failure or rotor loss, the drag on the low pressure system may be greatly reduced. A relatively high amount of energy (i.e., carryover energy) within the core may drive the low pressure system to rotate at relatively dangerous rotational speeds subsequent to the loss of such drag, despite a reduction in a fuel flow to the core. In order to ensure the low pressure system does not fail in such a failure condition, the low pressure system is designed to accept the carryover energy from the core in a loss of load condition, and more particularly, a turbine of the low pressure system is designed to be able to rotate at higher rotational speeds than would otherwise be necessary. However, such may lead to a relatively heavy, large, and expensive low pressure system, or more particularly, a relatively large bore within the turbine of the low pressure system.
Accordingly, a propulsion system capable of reducing a size of one or more components of the low pressure system without compromising the low pressure system's ability to function subsequent to a loss of load condition would be useful.